Enclosable evaporator/defroster unit for a refrigerated display case

ABSTRACT

The invention is for an enclosable evaporator/defroster unit for a refrigerated display case. The refrigerated display case has a cabinet with a floor, a ceiling, a front wall, a rear wall, and side walls. There is an access opening in one of the front wall, the rear wall and the side walls. An air duct extends around the cabinet for conducting a current of air. The air duct forms a substantially closed conduit. There is a gap in the conduit that coincides with the access opening in the cabinet. A fan circulates air in the air duct. An evaporator coil is positioned in the air duct to cool the circulating air. A defroster unit is also positioned near the evaporator coils to melt the condensation on the evaporator coil. The defroster unit has a heater, dampers, and an actuator for moving the dampers between an open and a closed position.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to refrigerated display cases and, moreparticularly but not by way of limitation, to evaporator coil defrostersassociated with such display cases.

[0003] 2. Discussion

[0004] Retailers use refrigerated display cases predominantly formerchandising of food, but also for other perishable items, such asflowers. Frozen food refrigerated display cases are maintained at lowtemperatures at about 0° F. Ice cream refrigerated display cases aremaintained in the range of −15° F. to −10° F. Because of the relativelyhigh refrigeration demand for frozen foods and ice cream, retailerscommonly keep these items in glass-door, reach-in coolers. However, fordisplay purposes, some retailers find the open front, multi-deck displaycases to be preferable. In the medium temperature range of 20° F. to 40°F., retailers prefer to use glass-door display cases for freshly cutmeats, cheeses and other delicatessen items, while they prefer to useopen front display cases for packaged meats and dairy products.

[0005] There are certain features required for all type of refrigerateddisplay cases. First, all refrigerated display cases have arefrigeration system that cools the product. This is typically done bypositioning an evaporator coil in a conduit and circulating air throughthe conduit. The evaporator coil contains cold refrigerant flowingthrough it and exchanges heat with the warmer circulating air in theconduit. The conduit surrounds a cabinet that holds the refrigeratedobjects.

[0006] A second feature that all refrigerated display cases have is anapparatus for defrosting the evaporator coils. Moisture in the conduitair condenses on the cold evaporator coils and interferes with the heattransfer between the cold refrigerant in the evaporator coils and theconduit air. This in turn causes an increased need for energy input intothe refrigeration system. As a result, all refrigerated display caseshave defroster heaters, usually electric or hot gas, to melt the frozencondensation on the evaporator coils.

[0007] Refrigerated display cases generally have two cycles ofoperation: a refrigeration cycle and a defrost cycle. During therefrigeration cycle, the refrigeration system operates and the defrostheater is idle. During the defrost cycle, the refrigeration system shutsdown and the defroster heater operates. Many systems also have an idle,non-operational mode in which neither the refrigeration system nor thedefroster system operates.

[0008] For an ideally designed system in the absence of any defrostingrequirements, a refrigeration system operates at its maximum efficiencywhen it runs all the time to maintain a design air temperature at somepoint in the system. The refrigeration system will lose efficiency everytime it has to cycle between an idle mode to an operating mode tomaintain the air design temperature. It will also lose efficiency thelonger the time it is in the idle mode. As a result, when arefrigeration system has to shut down to defrost the evaporator coil,the refrigeration system will be less efficient the longer it has toremain idle. Thus, it is desirable to minimize the time of the defrostcycle. For a long defrost cycle, there is also a greater likelihood forspoilage of product, especially for frozen foods.

[0009] There have been many inventions directed to improving theoperation of refrigerated display cases with defrosters. For exampleU.S. Pat. No. 4,239,518 issued to Steelman discloses a refrigerated casewith a movable fan that draws ambient air past the evaporator coil.

[0010] U.S. Pat. No. 5,669,222 issued to Jaster et al. discloses adefroster system in which an evaporator coil is heated by thecondensation of the refrigerant supplied by a compressor used in therefrigeration process.

[0011] U.S. Pat. No. 4,312,190 issued to Ibrahim et al. (Ibrahim '190)discloses a refrigerated glass door merchandiser for which a heat trapprevents heat generated during a defrost cycle from flowing back intothe refrigerated display section. The heat trap is a labyrinth structurethat, during the defrost cycle, prevents air in a conduit from flowingback through a fan for circulating air through the conduit.

[0012] The heat trap of Ibrahim '190 partially addresses the need toisolate the heat and vapor generated by a defroster heater from thedisplay section of the refrigerated merchandiser. However, therefrigerated display case of Ibrahim '190 allows warm ambient air toinfiltrate the refrigeration system because it shuts off the fan duringa defrost cycle.

[0013] Thus, there is a continuing need for a providing a defrostersystem for a refrigerated display case that lowers the energyrequirements of the refrigeration system while meeting all therequirements of the refrigeration system for preserving food and otherperishable items.

SUMMARY OF THE INVENTION

[0014] The advantages and features of the present invention will beapparent from the following description when read in conjunction withthe accompanying drawings and appended claims.

[0015] The invention is for a refrigerated display case with a displaysection for displaying refrigerated objects. The refrigerated displaycase has a cabinet with a floor, a ceiling, a front wall, side walls andan access opening to access refrigerated objects. There is an air ductextending around the cabinet for conducting a current of air thatcirculates in the air duct. The air duct forms a substantially closedconduit, but has a conduit gap substantially coincident with the accessopening. The air duct has an inlet and an outlet on opposed sides of theconduit gap. A fan is positioned in the air duct near the air inlet forcirculating the air through the conduit. A cold evaporator coil of arefrigeration system is positioned in the air duct. When the warmer aircirculates past the evaporator coils, there is an exchange of heatbetween cold refrigerant in the coils and the air.

[0016] A defroster unit is positioned in the air duct near the coils.The defroster heater melts frozen condensate from the coils during adefrost cycle. During the defrost cycle, an actuator closes dampers toenclose a defroster heater and the evaporator coil. The closing of thedampers retards heat transfer from the space near the evaporator coil,which reduces a heat gain by the refrigerated objects in therefrigerated display case. Thus, there is a net reduction of energyrequired to refrigerate the display case and a reduction in the amountof lost refrigeration product due to heating.

[0017] The advantages, and features of the present invention will beapparent from the description below when read in conjunction with thedrawings and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a side view of a refrigerated display case of thepresent invention.

[0019]FIG. 2 is a side view of a refrigerated display case of thepresent invention.

[0020]FIG. 3 is a side view of a refrigerated display case of thepresent invention.

[0021]FIG. 4 is a schematic representation of a refrigeration unit asembodied by the present invention.

[0022]FIG. 5 is a side view of one embodiment of an evaporator enclosurefor containing evaporator coil and a defroster heater.

[0023]FIG. 6 is a front view of one embodiment of an evaporatorenclosure for containing evaporator coil and a defroster heater.

[0024]FIG. 7 is a side view of one embodiment of an evaporator enclosurefor containing evaporator coil and a defroster heater.

[0025]FIG. 8 is a front view of one embodiment of an evaporatorenclosure for containing evaporator coil and a defroster heater.

DESCRIPTION

[0026] Referring to FIG. 1, a refrigerated display case 10 has a cabinet12, about which refrigerated air circulates to refrigerate the cabinet12. A layer of thermal insulation 13 is positioned on the periphery ofthe cabinet 12. The refrigerated air flows through an air duet 14 thatforms a substantially closed circular path. The cabinet 12 has an accessopening 16 for a person to access refrigerated objects displayed in thecase 10. The cabinet also has a floor 18, a ceiling 20, a r ear interiorwall 22, and side walls (not shown in FIG. 1). In some embodiments, aglass door may cover the access opening 16. Refrigerated objects, suchas meat, milk or ice cream, are placed in a display section 24 of thecase 10.

[0027] During a refrigeration cycle, air is drawn into the air duct 14at inlet opening 26 by the electric fan 28. Hinged dampers 30 and 32 arein an open position so that air moves through an evaporator unit 34.Actuators 36 and 38 move the dampers 30 and 32, respectively, from anopen position to a closed position (as shown in FIG. 2 below). As airmoves past a cold evaporator coil 40 in the evaporator unit 34, a heatexchange occurs between the relative warm air and cold refrigerant inthe evaporator coil 40. During the refrigeration cycle, a defrosterheater 42 does not operate and air does not enter the lower space 44 ofthe air duct 14. The lower space 44 should have a height of at least 3inches in order to ensure sufficient space for flow of air through theair duct 14.

[0028] The cold air from the evaporator unit 34 rises in the air duct 14behind the rear wall 22, passes through the air duct 14 above theceiling 20, and exits the air duct 14 at the outlet opening 46. The coldair in the air duct 14 refrigerates the floor 18, the rear wall 22, theceiling 20 and, in turn, the display section 24. Air exiting the outletopening 46 forms an air curtain 48 in an air duct gap 50 because of thevacuum pressure created by the fan 28 at the inlet 26.

[0029] For the present embodiment, the air duct gap 50 coincides withthe access opening 16. However, it is contemplated that for variousembodiments, the air duct gap 50 would not necessarily coincide with theaccess opening 16. Under normal conditions, the flow in the air curtain48 is not too strong, so that a person may comfortably accessrefrigerated objects in the refrigerated display case 10. However, theair flow should be sufficiently strong to prevent too much warm ambientair from entering the inlet 26.

[0030] FIGS. 2 shows the same embodiment of the refrigerated displaycase 10 as in FIG. 1 at a different time of operation. FIG. 2 shows therefrigerated display case 10 just after a refrigeration cycle has endedand just before a defrost cycle has begun. As shown in FIG. 2, theactuators 36 and 38 are moving the dampers 30 and 32, respectively, fromthe open position to a closed position. The electric fan 28 continues toturn because the air in the air duct 14 is protected from heat gain, asdescribed below. Although not shown in FIG. 2, refrigerant has stoppedcirculating through the evaporator coil 40.

[0031]FIG. 3 shows the same embodiment of a refrigerated display case 10as in FIGS. 1 and 2 during a defrost cycle. As shown in FIG. 3, theactuators 36 and 38 have moved the dampers 30 and 32, respectively, fromthe open position to the closed position. The electric fan 28 continuesto turn because the air in the air duct 14 is protected from heat gain,as described below. Although not shown in FIG. 3, refrigerant hasstopped circulating through the evaporator coil 40. The defroster heater42 has now activated.

[0032] The defroster heater 42 may be an electric heater or a hot gasheater. It is positioned near the evaporator coil 40 to melt any frozencondensation that has accumulated during the refrigeration cycle. Areflective material 52 is applied to an inside surface of the generallybox-like evaporator enclosure 54 of the evaporator unit 34 to inwardlyreflect radiation emanating from the defroster heater 42. The reflectivematerial 52 may be a reflective paint, reflective tape or a separatepiece made from a reflective substance, such as aluminum or stainlesssteel. Furthermore, an insulating material 56 (best seen in FIGS. 5-8)is applied to the outside of the evaporator enclosure 54 to retard heattransfer from the evaporator enclosure 54 by both heat conduction andheat convection. Water produced by the defrosting of the evaporator coil40 drains through a drain (not shown).

[0033] It is important to note that providing the evaporator enclosure54 around the evaporator unit 34 reduces the amount of energy requiredto melt the frozen condensation from the evaporator coil 40. Thisresults, in part, from the retention of heat by the evaporator enclosure54 because of the use of the reflective material 52 and the insulatingmaterial 56. This reduction of required energy is also due in part tothe closing of the dampers 30 and 32, which prevents air flow and heatconvection away from the evaporator coil 40.

[0034] It is also important that the defroster heater 42 is locatedclose to the evaporator coil 40 and that the defroster heater 42 isenclosed in the evaporator enclosure 54. This allows the defrosterheater 42 to melt the condensation on the evaporator coil 40 by acombination of radiative heat transfer, free convective heat transferand, to a small degree, conduction heat transfer. Free convection relieson the thermal currents generated by the heat from the defroster heater42 to move the air within the evaporator enclosure 54. As a result, itis not necessary to generate secondary air currents flowing through theevaporator enclosure 54 to melt the frozen condensation by forcedconvection. The time required to defrost the evaporator coil 40 isgreatly reduced when compared to the time required for defroster systemswithout an evaporator enclosure 54.

[0035] As a result, the efficiency losses associated with having to shutthe refrigeration system down during a longer defrost cycle are alsoreduced. Thus, the energy savings are much greater than the energy thatwould be saved just by running the defrost heater a shorter period oftime.

[0036] Another important feature of the embodiment shown in FIGS. 1-3 isthat, during either the defrost mode or in the refrigeration mode, theair current in the air duct 14 is maintained in a single continuouscirculatory path. That is, it is not necessary to divert the flow intomultiple currents to melt the condensation on the evaporator coil 40.This helps to maintain the flow without the use of additional fansneeded to circulate the air through multiple paths.

[0037] In FIG. 4, a schematic representation is shown of the operationof the mechanical components of the refrigeration system used to coolthe refrigerated display case 1 0. Gaseous refrigerant is compressed ina compressor 60. The refrigerant passes then through a condenser coil62, over which a fan 64 blows cool ambient air, to remove heat. Theremoval of heat from the refrigerant causes it to condense into aliquid.

[0038] The liquid refrigerant then flows through a metering device 68where it expands to a gas and moves through the evaporator coil 40. Therefrigerant absorbs heat in changing from a liquid to a gas, causing theair that is blown over the coil 40 by the fan 28 to cool. The expandedgas exits the evaporator coil 40 and through a solenoid valve 66 thatshuts off the flow of refrigerant during a defrost cycle. The expandedgas refrigerant returns to the compressor 60 to begin the refrigerationcycle again.

[0039]FIGS. 5 and 6 show the evaporator enclosure 54 that surrounds theevaporator unit 34. The evaporator enclosure 54 is normally open and thedampers 30 and 32 are in an open position during a refrigeration cycle.As shown in FIGS. 5 and 6, the dampers 30 and 32 are in the closedposition. All of the interior walls of the evaporator enclosure 54 arecovered with reflective material 52. All of the exterior walls of theevaporator enclosure 54 are covered with an insulating material 56,including the dampers 30 and 32. Two electric motors 36A and 38A act asactuators to move the dampers 30 and 32 between the open and closedposition, respectively. Although two electric motors 36A and 38A areshown in FIGS. 5 and 6, the actuators 36 and 38 could be hydraulicmotors, or a single electric motor combined with a mechanical linkage.

[0040] As shown in FIG. 6, the damper 30 is rigidly attached to an axle55. The electric motor 36A has a drive shaft 37 coupled to the axle 55.Rotation of the motor drive shaft 37 causes the axle 55 to also rotateand causes the damper 30 to move to an open or closed position. In oneembodiment, the non-hinged ends of the dampers 30 and 32 engage acompressible material in closing and form a tight seal to preventleakage of heat by convection.

[0041]FIGS. 7 and 8 show an alternative embodiment of the evaporatorenclosure 54 that surrounds the evaporator unit 34. The evaporatorenclosure 54 is normally open and the dampers 30 and 32 are in an openposition during a refrigeration cycle. As shown in FIG. 7, the damper 32is in the closed position. In FIG. 7, the damper 30 is in a partiallyopen position merely for purposes of illustrating the movement of thedampers 30 and 32. All of the interior walls of the evaporator enclosure54 are covered with reflective material 52. All of the exterior walls ofthe evaporator enclosure 54 are covered with an insulating material 56,including the dampers 30 and 32.

[0042] Bimetal coil actuators 36B and 38B move the dampers 30 and 32,respectively, from an open position and a closed position. The bimetalcoil actuators have the property of expanding and contracting theirspiral coil in response to temperature changes. As seen in FIG. 8, at aninterior end, the coil 36B is connected to a first pin 37B, which is inturn rigidly connected to the bottom of the enclosure. At an exteriorend, the coil 36B is connected to a second pin 39B, which in turn isrigidly connected to the damper 30. An internal, electric heatingelement (not shown) heats the bimetal coil 36B causing it to expand andmove the damper 30 to the open position. Shutting off electrical powerto the internal heating element causes the bimetal coil 36B to cool andretract the damper 30 to the closed position.

[0043] For purposes of the claims that follow, a defroster unit isdefined to be the defroster heater 42, the hinged dampers 30 and 32, andthe actuators 36 and 38 that move the dampers 30 and 32.

[0044] It is clear that the present invention is well adapted to carryout the objects and to attain the ends and advantages mentioned as wellas those inherent therein. While presently preferred embodiments of theinvention have been described in varying detail for purposes of thedisclosure, it will be understood that numerous changes may be madewhich will readily suggest themselves to those skilled in the art andwhich are encompassed within the spirit of the invention disclosed andas defined in the above text and in the accompanying drawings.

What is claimed is:
 1. A refrigerated display case with a displaysection for displaying refrigerated objects, comprising: (a) a cabinethaving a floor, a ceiling, a front wall, a rear wall, side walls and anaccess opening in one of the front wall, the rear wall, and the sidewalls, wherein the access opening provides access to the refrigeratedobjects; (b) an air duct extending around the cabinet for conducting acurrent of air, wherein: (i) the air duct forms a substantially closedconduit with a conduit gap substantially coincident with the accessopening in the cabinet; and (ii) the air duct has an inlet opening andan outlet opening at opposed sides of the conduit gap; (c) a fan forcirculating air through the duct, such that an air curtain isestablished between the inlet opening and the outlet opening; (d) anevaporator coil positioned in the air duct, wherein, during arefrigeration cycle, a refrigerant expands in the evaporator coil andthe fan causes air to flow over the evaporator coil resulting in anexchange of heat between the air in the duct and the cold refrigerant;and (e) a defroster unit comprising: (i) a heater for meltingcondensation on an outside of the evaporator coil; (ii) hinged dampers;and (iii) an actuator for moving the dampers from an open positionduring the refrigeration cycle to a closed position during a defrostcycle.
 2. The refrigerated display case of claim 1 wherein moving thedampers from the open position to the closed position provides anevaporator enclosure and retards heat transfer from the space near theevaporator coil.
 3. The refrigerated display case of claim 1 wherein theactuator to move the dampers is an electric motor.
 4. The refrigerateddisplay case of claim 1 wherein the actuator to move the dampers is abimetal coil.
 5. The refrigerated display case of claim 2 furthercomprising a reflective material to cover the interior walls of theevaporator enclosure.
 6. The refrigerated display case of claim 2further comprising an insulating material to cover the exterior walls ofthe evaporator enclosure.
 7. The refrigerated display case of claim 1wherein, during the refrigeration cycle and the defrost cycle, thecurrent of air in the air duct forms a single continuous circulatorypath.
 8. A defroster unit for a refrigerated display case with anevaporator coil positioned in an air duct, the defroster unitcomprising: (a) a heater for heating an outside of the evaporator coilto melt frozen condensation accumulated thereon; (b) a pair of damperspositioned inside the air duct; and (c) an actuator for moving thedampers from an open position during a refrigeration cycle to a closedposition during a defrost cycle.
 9. The defroster unit of claim 8wherein moving the dampers from the open position to the closed positionprovides an evaporator enclosure for the evaporator unit and thedefroster heater and wherein the evaporator enclosure retards heattransfer from the space near the evaporator coil.
 10. The defroster unitof claim 8 wherein the actuator is an electric motor.
 11. The defrosterunit of claim 8 wherein the actuator is a bimetal coil.
 12. Thedefroster unit of claim 9 further comprising a reflective material tocover the interior walls of the evaporator enclosure.
 13. The defrosterunit of claim 9 further comprising an insulating material to cover theexterior walls of the evaporator enclosure.
 14. In a refrigerateddisplay case having air circulating in an air duct with an evaporatorcoil located in the air duct and having a defrost heater located nearthe evaporator coil, a method for preventing the heat generated during adefrost cycle from causing food spoilage, the method comprising: (a)positioning the evaporator coil and the defrost heater in an evaporatorenclosure within the air duct wherein the evaporator enclosure can beopened or closed by moving dampers to an open or closed position; (b)moving the dampers to an open position during a refrigeration cycle ofoperation of the refrigerated display case; and (c) moving the dampersto a closed position during a defrost cycle of operation of therefrigerated display case.
 15. The method of claim 14 wherein anactuator moves the dampers to an open position or a closed position. 16.The method of claim 15 wherein the actuator is an electric motor. 17.The method of claim 15 wherein the actuator is a bimetal coil.
 18. Themethod of claim 15 wherein the actuator is a hydraulic motor.